With the progress of the human genome project, a movement to understand a living body at the DNA level and utilize the knowledge thus obtained for disease screening or understanding of the life phenomenon has become active. Investigation of a gene expression condition is effective for understanding of the life phenomenon or genetic activity. As a powerful method for finding the gene expression condition, a so-called DNA chip, that is, a probe array having a number of DNA probes divided by kind and immobilized on a surface of a solid such as slide glass has recently been employed. Examples of a manufacturing method of a DNA chip include a method of synthesizing base oligomers having a designed sequence one by one in a plurality of divided cells by using photochemical reaction and lithography widely employed in a semiconductor industry (Science, 251, 767-773 (1991)) and a method of embedding plural kinds of DNA probes in sections, one probe in one section (Science, 270, 467-470 (1995); Nat. Biotechnol. 18, 438-441 (2000)).
Manufacture of a DNA chip by either one of the above-methods takes labor and time, leading to a high cost, because DNA probes must be immobilized onto respective arrays or base oligmers must be synthesized one by one in each array. These methods are accompanied with the drawbacks that the density of the probes differs with the section because they are disposed as liquid drops on the surface of a solid, combination of probe kinds cannot be easily changed, and manipulation of them is difficult for users.
With a view to overcoming the above-described problems, probe array having plural kinds of beads each having a DNA probe fixed thereon, that is, a bead array (Clinical Chemistry, 43, 1749-1756 (1997); Science 287, 451-452 (2000); Nucleic Acids Research 30, e87 (2002)) were proposed. When beads are used, a probe array free from variations in probe density by bead can be manufactured, because a chemical reaction in a solution can be utilized for the immobilization of the probe.
In a DNA chip, the kind of a probe is discriminated by the position where an oligomer is prepared or spotting position of each DNA probe or protein probe, while in the probe array using probe-immobilized beads, it is discriminated by using beads different in color (Clinical Chemistry, 43, 1749-1756 (1997); Science, 287, 451-452 (2000)) or by the arraying order of beads in the capillary (Nucleic Acids Research 30, e87 (2002)).
In a DNA chip, a sample to be analyzed is reacted with an oligomer or DNA immobilized onto the DNA chip while spending a half a day or all day for identification and quantitative analysis of plural kinds of DNAs contained in the sample. In a probe array having beads arranged in a capillary, that is, a bead array, on the other hand, a sample to be analyzed is forced to flow in a capillary. Bead array needs less time for genetic testing than the conventional method so that it is a measuring technique suited for use in medical sites such as hospitals. For example, in an infection requiring urgent diagnosis or a bacterial test, it is expected as rapid detecting means of an exogenous gene of a pathogenic microorganism genome not existing in the genome of the patient.
For industrialization of a bead array, it is essential to establish a method capable of selecting desired probe-immobilized beads, depending on the purpose of the test, and arraying them freely. A method of pouring beads, under control, in a capillary one by one by making use of the flow of a liquid (Japanese Patent Application Laid-Open No. Hei 11-243997); and a method of retaining one bead, among a plurality of beads introduced together with a solvent, in a microhole made in a sheet and permitting insertion of only one bead, transferring the sheet to a capillary or groove formed in a plate, and thus arranging the beads one by one (Japanese Patent Application Laid-Open No. 2000-346842) were proposed so far.    Non-patent Document 1: Science, 251, 767-773 (1991)    Non-patent Document 2: Science, 270, 467-470 (1995)    Non-patent Document 3: Nat. Biotechnol. 18, 438-441 (2000)    Non-patent Document 4: Clinical Chemistry, 43, 1749-1756 (1997)    Non-patent Document 5: Science, 287, 451-452 (2000),    Non-patent Document 6: (Nucleic Acids Research 30, e87 (2002)    Patent Document 1: Japanese Patent Application Laid-Open No. Hei 11-243997    Patent Document 2: Japanese Patent Application Laid-Open No. 2000-346842